The present invention relates to a pilot operated flow regulating valve. Such valves are used to regulate the flow of a fluid by maintaining a constant differential pressure between the upstream and the downstream side of the valve seat. Typical applications of said valves are; the regulation of the flow of heated pressurized water passing a pressure loss generating heat exchanger, regulation of the flow of refrigerant through an expansion valve in a refrigerating cycle using carbon dioxide as s refrigerant, regulation of the fuel rate through a controllable fuel injection valve for direct injection in an internal combustion engine, etc., i.e. applications where the fluid at least temporarily undergoes a great pressure differential.
Due to the fact that such valves when directly actuated by a solenoid would need a huge solenoid in case of a differential pressure of about 50 to 100 times the atmospheric pressure or more, instead pilot operated regulating valves are used in which the pilot valve only needs a small solenoid and actuates the main valve member by fluid pressure. Conventionally, in such pilot operated flow regulating valves a pilot route extends between the downstream side of the valve seat and the pressure governing chamber. The main valve member is opened and closed from the downstream side assisted by a constant pressure differential control valve actuated by said solenoid. The passage at the upstream side of the valve seat and the pressure governing chamber communicate with another via a leak route of small cross-section. However, the pressure governing chamber via said leak route then holds high pressure in relation to the downstream pressure when the pilot route is closed during main valve closing. Due to the high pressure differential fluid will then flow from pressure governing chamber to the downstream side through the pilot route and its vicinities and a flow larger than a certain degree always occurs inconveniently.
Furthermore, in a pilot operated flow regulating valve as known the initial fluid pressure does not act to generate a closing force at the main valve member in a state where the main valve member has reached its fully closed state so that a relatively strong spring is necessary to retain said fully closed state. Then, in order to open the main valve member again, an operating differential pressure stronger than the force of the spring must be produced. Said operating differential pressure reduces the fluid pressure as controlled by the flow regulating valve, because the valve does not respond unless the initial fluid pressure is sufficiently high to compensate said pressure loss and to overcome the force of the spring. This is an apparent shortcoming, particularly when the initial pressure of the fluid at the upstream side is low. The entire operable pressure range is limited.
It is an object of the invention to provide a pilot operated flow regulating valve of the kind as disclosed eliminating the drawbacks of conventional valves, such that the pilot operated flow regulating valve has an improved operational performance, does not need undesirable high differential pressure for response and eliminates the danger of undesirable leakage flows in the closed state. It is a part of said object to create a pilot operated flow regulating valve capable of definitely stopping a flow of fluid to the downstream side when the pilot route is closed, even though the upstream fluid pressure is high. Furthermore, a pilot operated flow regulating valve is to be provided having a good pressure efficiency and does not cause undesirable pressure losses in the fluid.
Said objects can be achieved with the features as contained in claim 1, in claim 2 and in claim 8.
The respective actuation of the constant differential pressure control valve is necessary, either to open or close the main valve member or to adjust its relative position at the valve seat for the desired constant fluid flow. This operational performance is achieved without an undesirable pressure loss, because the leak route allows to relieve the pressure in the pressure governing chamber sufficiently to open the main valve member without a significant pressure loss. Furthermore, since the constant differential pressure control valve selectively also can be brought in a blocking position the pilot route will be reliably blocked avoiding any undesired leak flow from the high pressure side to the low pressure side even in case of extreme high inlet pressure.
In the valve according to claim 2 the flow through the valve seat can reliably be controlled by controlling the constant differential pressure valve. Since the inside of the pressure governing chamber can have a low pressure as also the passage at the downstream side, no leakage flow occurs from the pressure governing chamber to the downstream side even though the pressure in the passage at the upstream side may be extremely high. Since also the pilot route can be blocked totally any flow of fluid to the downstream side can be stopped definitely.
For the valve as disclosed in claim 8 the pressure loss inevitably created by the heat exchanger can be utilised to operate the flow regulating valve. This is carried out by connecting the pressure governing chamber via the leak route with one of the fluid pipelines at the upstream or downstream side of the heat exchanger, while the constant differential pressure control valve is situated between the respective other pipeline and the pressure governing chamber. There is no undesirable pressure loss necessary for operating the flow regulating valve. A very reliable operation performance can be obtained even in a case where the initial fluid pressure at the upstream side is low. The flow regulating valve shows a good pressure efficiency without creating significant fluid pressure losses.
Preferred embodiments are contained in the depending claims.